Today's lab
Goals for today:
- practice problems similar to what will be on the midterm exam
- Where you see this icon, you can click it to check the problem in
Practice-It!
Exercise : Expressions
For each expression in the left-hand column, indicate its value in the right-hand column. Be sure to list a constant of appropriate type (e.g., 7.0 rather than 7 for a double, Strings in quotes).
12/5 + 8/4
|
4 |
|
2.5 * 2 + 17/4
|
9.0 |
|
41 % 15 % 7 + 17 % 3
|
6 |
|
21/2 + "7 % 3" + 17 % 4
|
"107 % 31" |
|
46/3/2.0/3 * 4/5
|
2.0 |
Exercise : Parameter Mystery
-
Fill in the boxes with the output that each method call would produce:
public class Mystery { public static void main(String[] args) { String hear = "bad"; String song = "good"; String good = "hear"; String walk = "talk"; String talk = "feel"; String feel = "walk"; claim(feel, song, feel); // to walk the walk is good claim(good, hear, song); // to hear the good is bad claim(talk, "song", feel); // to feel the walk is song claim("claim", talk, walk); // to claim the talk is feel } public static void claim(String hear, String good, String song) { System.out.println("to " + hear + " the " + song + " is " + good); } }
Exercise :
if/else mystery
Consider the following Java code.
public static void ifElseMystery(int a, int b) {
if (a < b) {
a = a * 2;
}
if (a > b) {
a = a - 10;
} else {
b++;
}
System.out.println(a + " " + b);
}
Fill in the boxes with the output produced by each of the method calls.
ifElseMystery(10, 3);
|
0 3 |
|
ifElseMystery(6, 6);
|
6 7 |
|
ifElseMystery(3, 4);
|
-4 4 |
|
ifElseMystery(4, 20);
|
8 21 |
Exercise : while loop mystery
Fill in the boxes at right with the output produced by each method call.
public static void mystery4(int n) {
int x = 1;
int y = 2;
while (y < n) {
if (n % y == 0) {
n = n / y;
x++;
} else {
y++;
}
}
System.out.println(x + " " + n);
}
|
|
Exercise : assertions
Identify whether each assertion is always/never/sometimes true
at each point.
public static void mystery(int x, int y) {
int z = 0;
// Point A
while (x != y) {
// Point B
z++;
if (x > y) {
// Point C
x = x / 10;
} else {
// Point D
y = y / 10;
}
}
// Point E
System.out.println(x + " " + y + " " + z);
}
Solve this problem in Practice-It by clicking on the check-mark above.
Exercise : before
Write a method before that takes as parameters two month/day
combinations and that returns whether or not the first date comes before
the second date (true if the first month/day comes before the
second month/day, false if it does not). The method will take
four integers as parameters that represent the two month/day combinations.
The first integer in each pair represents the month and will be a value between 1 and 12 (1 for January, 2 for February, etc, up to 12 for December). The second integer in each pair represents the day of the month (a value between 1 and 31). One date is considered to come before another if it comes earlier in the year.
Solve this problem in Practice-It by clicking on the check-mark above.
Exercise : printFactors
-
Write a method named
printFactorsthat accepts an integer as its parameter and uses a fencepost loop to print the factors of that number, separated by the word"and". For example, the callprintFactors(24)should print the following output:1 and 2 and 3 and 4 and 6 and 8 and 12 and 24
- You may assume that the parameter value passed is greater than 0.
- (Hint: This is an example of a fencepost problem.)
- Try solving this problem in Practice-It! using the link above.
Exercise : sameDashes
Write a method sameDashes that takes two strings as parameters
and that returns whether or not they have dashes in the same places
(returning true if they do and returning false
otherwise). For example, below are four pairs of strings of equal length
that have the same pattern of dashes. Notice that the last pair has no
dashes at all.
string 1: "hi--there-you." "-15-389" "criminal-plan" "abc" string 2: "12--(134)-7539" "-xy-zzy" "(206)555-1384" "9.8"To be considered a match, the strings must have exactly the same number of dashes in exactly the same positions. The Strings might be of different length.
Solve this problem in Practice-It by clicking on the check-mark above.
Exercise : allDigitsOdd
Write a method named allDigitsOdd that returns whether every
digit of a positive integer is odd. Your method should
return true if the number consists entirely of odd digits
and false if any of its digits are even. 0, 2, 4, 6, and 8
are even digits, and 1, 3, 5, 7, 9 are odd digits.
For example, allDigitsOdd(135319) returns true
but allDigitsOdd(9145293)
returns false.
Hint: You can pull apart a number into its digits using /
10 and % 10.
Exercise : season
-
Write a method named
seasonthat takes two integers as parameters representing a month and day and that returns a String indicating the season for that month and day. Assume that months are specified as an integer between 1 and 12 (1 for January, 2 for February, and so on) and that the day of the month is a number between 1 and 31. -
If the date falls between 12/16 and 3/15, you should
return
"Winter". If the date falls between 3/16 and 6/15, you should return"Spring". If the date falls between 6/16 and 9/15, you should return"Summer". And if the date falls between 9/16 and 12/15, you should return"Fall". - Try solving this problem in Practice-It! using the link above.
Exercise : firstDigit
-
Write a method named
firstDigitthat returns the first digit of an integer. For example,firstDigit(3572)should return3. It should work for negative numbers as well. For example,firstDigit(-947)should return9. - Try solving this problem in Practice-It! using the link above.
- (Hint: This problem requires a loop.)
Exercise : makeGuesses
Write a method named makeGuesses that will output random
numbers between 1 and 50 inclusive until it outputs one of at least 48.
Output each guess and the total number of guesses made. Below is a sample
execution:
guess = 43 guess = 47 guess = 45 guess = 27 guess = 49 total guesses = 5
Try solving this problem in Practice-It! from the link above.